A number of mechanical screws and fasteners are used to fuse, fixate or fasten to bone. Such fasteners are used particularly frequently in correcting spinal problems. One well known set of mechanical fasteners includes pedicle screw assemblies which are used to align and/or fix a desired spatial relationship between vertebral bodies. Pedicle screws have a shape and size that is configured to attach to pedicle bone. Pedicle screw assemblies typically include a threaded shank that is adapted to be threaded into a vertebra, and a receiving member usually in the form of a U-shaped head.
Referring to FIG. 1, a known reduction screw style pedicle screw assembly 1 is illustrated. Pedicle screws used for spinal surgery generally include a shank 3 and a receiving member 5. Receiving member 5 typically includes a U-Shaped head 7 from which two opposing arms 9 extend. In some prior art pedicle screw assemblies, extended portions 11 are permanently (with a frangible connection) or removably attached to and extend upwardly from the opposing arms 9. Shown in FIG. 1 are distal frangible connection points 10 attaching the extended portions 11 to opposing arms 9. Such distal frangible connection points 10 may be used to break off extended portions 11 from the reduction screw leaving the opposing arms 9, U-shaped head 7 and shank 3. An ordinarily skilled artisan that distal frangible connection points may be utilized on any style of reduction screw assemblies or mechanical fastening systems having the general shape of a shank and receiving member.
A set-screw, plug, or similar type of fastening mechanism is used to lock the spinal connector, e.g., a spinal rod, into the receiving head of the pedicle screw. In use, the shank of each screw is threaded into a vertebra, and once properly positioned, a rod is seated through the receiving member of each screw and the rod is locked in place by tightening a cap or other fastener mechanism to securely interconnect each screw and the spinal rod.
In general, pedicle screw assemblies use two or more pedicle screws which are secured to vertebra. After the screws are secured to the vertebra, the screws are coupled to a spinal stabilization rod that restricts movement of the stabilized vertebra. It is important that the screws have a secure coupling with the spinal stabilization rod in order to prevent movement of the rod relative to the screw after placement. The pedicle screws are coupled to the rods by way of the opposing arms of the receiving member.
One issue with the opposing arms of the receiving member is that they can splay, or spread apart while applying torque loads to the setscrew against the rod during what is commonly known as reduction and final tightening or torquing of the rod. Splaying can result in failure of the rod to remain in place relative to the shank portion.
A number of methods and structures have been employed to prevent splaying of the opposing arms of receiving members. Such structures include the use of a non-breakaway ring permanently affixed to the upper ends of the opposing arms (or extensions). When such structures are used, a surgeon must use a separate cutter to remove the ring upon completion of surgery so that the arms (or extensions) may be freed for removal. The cut portions are small, may be sharp and can become projectiles from the force of the cutting action.
In yet other known methods for preventing splaying, a ring is removably screwed or attached onto opposing arms (or extensions). Such methods require complex tools for manipulation of the ring and arms (or extensions).
What is needed is an anti-splay bridge which is removably coupled to the opposing arms (or extensions), and which may be readily removed without complex tools or manipulation and in a controlled manner.